Vehicles are increasingly being fitted with safety belt warning systems which, for a respective vehicle seat loaded by the weight of a person, generate a warning signal in the event that the safety belt is not done up. A conventional safety belt warning system includes for example a graphite composite-based sensor on a PET (e.g. polyethylene terephthalate) film with a contact dye of which the resistance varies as a function of the pressure applied. Because such a sensor is arranged under the seat cover, a number of problems arise. Thus the sensor affects the comfort when sitting. The design of the seat cover can have an effect on the performance of the sensor and so is subject to corresponding restrictions.
Also, the foam is subject to certain restrictions with respect to the surface design. Lastly, the behaviour of the sensor which depends on the humidity and/or ageing is critical as well.